Mac app dealing with safari web address

I need an app for the Mac which will be used when the user is pulling up a website in safari. So the app will need to be aware of what web address or URL the user is pulling up in the web browser. Once the app figures this out, It will show a small notification at the top of the screen showing some text that the user has previously setup. So here is an example...when the user goes to lets say [login to view URL], this app will show a small text line in a bubble at the top of the screen, after a certain time, it goes away. The app will need to be a menu bar item at the top of the screen. The app will need to have the ability to save the current URL when the user clicks save and it will then ask for the text the user wants to display once thenurl is loaded the next time and every time it is pulled up. Needs to be built in Xcode. Needs also a setting on how long the user wants the bubble with text to stay up.